1. Field of the Invention
This invention relates to a method and apparatus using a computer to control editing on video equipment, audio equipment, etc. (hereinafter referred to as "AV devices").
2. Background of the Invention
A control system for performing editing control for AV devices using a computer has been previously proposed in Japanese Patent Application No. 3-192640 by Kawamura.
In this control system, a personal computer (hereinafter referred to as "PC") is connected to the AV devices through a bidirectional communication line, and a control signal for controlling the operation of the AV devices is transmitted from the PC to the AV devices on the basis of a communication protocol called VISCA (Video System Control Architecture: Trademark), thereby performing the editing control for the AV devices.
One of the features of this control system is that both the PC and the AV devices have a clock having the same time, and a response signal transmitted from the AV equipment to the PC includes a time information of the clock in the AV devices. In this control system, the following operation is carried out when a video signal reproduced from a reproducing VTR is recorded by a recording VTR.
First, the PC supplies each of the reproducing VTR and the recording VTR with a control signal for rewinding a tape of each VTR from an editing point thereof by a predetermined time T, and setting each VTR to a pause mode. Subsequently, upon completion of the setting of the pause mode, the PC supplies these VTRs with a control signal for simultaneously releasing from pause mode at a predetermined time (hereinafter called the "pause-release setting time"). Subsequently, upon completion of the release of the VTRs from pause mode, the PC supplies each VTR with a control signal for inquiring about a tape position. Time information ,and the tape position of each VTR is transmitted to the PC. On the basis of the tape positions and the time information, the PC calculates a deviation of the tape position between the VTRs. If no deviation occurs in the tape position, the PC supplies the recording VTR with a control signal for setting the recording VTR to a recording mode at an instantaneous time when the predetermined time T elapses from the pause-release setting time. If a deviation occurs in the tape position, the tape position is adjusted by travelling the tape by a suitable amount (hereinafter referred to as "tape-travel adjustment"). The PC then supplies the recording VTR with the control signal for setting the recording mode in the same manner as described above. Through the above operation, a picture of the reproducing VTR which is subsequent to the editing point is recorded by the recording VTR.
In the control system as described above, however, even when the PC simultaneously supplies the reproducing and recording VTRs with the control signals to release from pause mode, the time when each of the reproducing and recording VTRs begins to advance its tape is delayed in accordance with the delay of rise-up of the mechanical system of each VTR.
Therefore, when the mechanical systems of the reproducing and recording VTRs have different rise-up times, these reproducing and recording VTRs are simultaneously released from the pause mode at a predetermined time, the tape positions of these VTRs are deviated due to the difference in rise-up time of the mechanical systems. Therefore, the tape-travel adjustment is required, and thus the timing to start a picture recording operation is delayed. Further, when the tape is edited without tape-travel adjustment, a head portion of a reproducing tape may not be recorded on a recording tape, or may be recorded superimposed on a portion of the recording tape where information has been already recorded. This is because of the deviation between the editing point of the reproducing tape and the editing point of the recording tape.